Each fungiform papilla contains a single taste bud in the rat and several of these provide input to a single chorda tympani nerve fiber. When the papillae supplying input to a fiber are simultaneously stimulated with chemical stimuli, lateral interaction can occur among the neural inputs. A depression of the single fiber response is elicited when an isolated papilla is individually stimulated with sodium chloride and the papillae around it are stimulated with potassium salts. When sodium chloride is applied to the single isolated papilla and simultaneously to the surround, the single fiber response is enhanced. Responses will be obtained from single chorda tympani fibers in the rat and the single papillae which supply input to the fiber will be mapped. The magnitude of the lateral depression on individual papillae will be determined by using potassium benzoate as the surround stimulus, and the magnitude of lateral enhancement will be determined by using NaCl as the surround stimulus. Following the electrophysiological experiment, the papillae will be excised and prepared for light microscopy or electron microscopy. The morphology of the nerve fibers in the excised papillae will be reconstructed using silver-stained light micrographs and electron micrographs. The result which is sought is an electrophysiological description of the interactions between several fungiform papillae and a reconstruction of the nerve fibers which interconnect the papillae. It is anticipated that these observations will lead to conclusions about the number and variety of neurons which elicit lateral taste interactions. This study should have direct relevance to the phenomenon of lateral interaction in other sensory systems and should provide a better understanding of the taste system as a basis for scientific, clinical, and technological utilization. BIBLIOGRAPHIC REFERENCES: Miller, Jr., Inglis J. "Taste bud distribution and regional responsiveness on the anterior tongue of the rat." Physiol. & Behav. 16: 439-444, 1976.